Al4(P(t)Bu2)6--a derivative of Al4H6--and other Al4 species: a challenge for bonding interpretation between Zintl ions and metalloid clusters.

The highly energetic molecule Al(4)H(6), with its distorted tetrahedral structure, was recently characterized via mass spectrometry and photoelectron spectroscopy investigations (Li, X.; et al. Science 2007, 315, 356). Here we present the preparation and structural investigation of the first analogous Al(4)R(6) cluster compound. In order to understand the bonding in this kind of Al(4) molecule, density functional theory and second-order Møller-Plesset perturbation theory calculations were performed. The results obtained are discussed in comparison with bonding in other Al(4) moieties, especially the aromatic bonding behavior in the dianionic planar Al(4)(2-) species (Li, X.; et al. Science 2001, 291, 859). Finally, on the basis of the results obtained for Al(4) species, a more general problem is discussed: the difference in bonding between Zintl ions and metalloid clusters.